An apparatus for the pervaporation separation of liquid mixtures can comprise a plurality of platelike components, which are assembled to form a structure that is similar to a filter stack in a filter press or a plate heat exchanger provided with individual cells. Each pervaporator cell can comprises a raw fluid compartment and a permeate compartment, which are separated by a vapor-permeable diaphragm.
For pervaporation, liquid mixtures are supplied to a diaphragm which has a much higher permeability for one or more components of the mixture than for the other components. One component which has a higher solubility and a higher diffusibility in the diaphragm matrix constitutes a permeate, which migrates or diffuses through the diaphragm from one side and can be withdrawn from its opposite side as vapor. A component having a lower solubility and diffusibility is retained as a retentate.
The separations which can thus be effected cannot be achieved at all or only at much higher cost by other methods. For instance, it has been proposed in U.S. Pat. No. 4,405,409 to remove water from mixtures of organic liquids and water by first reducing the water content by distillation and subsequently decreasing the water content further by pervaporation.
The separating effect of diaphragms used for pervaporation has long been known, but has not been used industrially on a substantial scale.
This has been due, inter alia, to the fact that each apparatus developed for pervaporation has been too expensive and/or has not been sufficiently reliable in operation.
Pervaporators comprising coiled structures are known in addition to the pervaporators described previously (see German Patent Publication DE-AS No. 29 02 247, Published German Application DE-OS No. 32 19 869 and Published German Application DE-OS No. 33 03 910).
The basic flat-plate design is similar to that of filter presses and plate heat exchangers. Substantially similar platelike components are joined in a pack or stack, in which all required connecting passages have been integrated by the provision of suitable bores and seals.
As far as I know, the known apparatus of this type has not been used on an industrial scale.
Plastic or synthetic resin structures may involve the problem that the platelike components cannot be made with the required small tolerances in relatively large sizes and that the material does not have an adequate creep strength and tends to flow under the high external pressures which are exerted by the tie rods and are required to ensure an adequate seal.
Metal structures have not been used before, probably because their manufacture is too expensive or because they lack an adequate resistance to corrosion. Besides, they cannot readily be adapted to different functions so that an integration as is provided in the apparatus described first hereinbefore is difficult.